The Roland SPD6 is a small drum pad and midi controller with on board sounds. I will not comment on the internal sounds, I have not used them since I tried out the unit in a shop once.
There are six Triggering pads of roughly equal size. The pads are very sensitive to velocity, allowing a dynamic performance. A small switch on the back changes the overall sensitivity of the pads from that suitable for sticks to that suitable for hands. I haven't TRied to play the unit with sticks and I wouldn't try, I'm not a proficient drummer and I imagine that the accuracy needed to hit such a small target is beyond me. Accuracy is important as well because practically, the pads are much smaller than they appear to be. If a pad is struck around it's edges then other sounds are triggered accidentally. There's roughly a 4 square inch area in the middle of the pads that's good to hit and never triggers any other notes. If you were playing with sticks though I imagine that the bounce on the pads would be quite pleasant.
At the rear of the unit there is a power supply socket (for a 100mA 9vDC power supply, which, rather annoyingly is not provided), two pedal switch inputs for conTRolling kicks or hi-hats, a volume switch (for the internal sounds), stereo outputs, a midi out (crucially), the sensitivity switch and a slot to attach a lap top lock to (an interesting touch which it would be nice to see become a trend).
Underneath there is a battery compartment for 6AAs (which seem to only last a disappointing time) but at least are supplied with the unit. there is also a large mounting space for putting the SPD6 on a stand, which Roland will happily sell you.
On the front there's a power button and eight buttons for selecting banks of sounds and programming the SPD6. I'm sure the different patches are great news if you're using the on-board sounds but they send notes that are very far apart from each other on a keyboard range so when using the unit to play a sampler things get complicated. The way I use it is to use a default template sampler program to drop sounds into, which is already configured to contain just the notes that the SPD6 triggers.
There is some way of setting your own preset configuration, but the manual doesn't help you by telling you which note numbers correspond to which midi notes, it really only discusses internal sounds and numbers them.
Imagine, though, my surprise when I connected the SPD6 to my MC303 (both manufactured by Roland) and started playing, only to find that the MC303 seizes up and needs re-booting each time. Clearly some kind of program change or other midi weirdness is happening. Oh well, I guess the drums sounds on my 303 will be very similar to the internal sounds, so maybe I'll use them one day, no seriously, I might do one day.
The other vaguely annoying thing is the gate time setting (0.1s, 1.0s, 2.0s or 4.0s). Yes you counted right, that's only four settings. What's more is the really annoying reality of having to set the gate time for each pad, each time you switch the unit on. This becomes tedious. It does send a note off when you trigger another note on the same pad though, so you don't get overlapping notes. the other issue of great annoyance is the precision of triggering. It always triggers a note when you hit it but sometimes it TRiggers more than one. This is actually less annoying when the note is on another key, at least then you can hear it. Sometimes, it can generate a minimum length midi note, bang underneath the main one. Editing these out from a long section of performance is tedious.
In praise of the SDP6 it has to be said that despite these (minor) annoyances in setting it up it does what it says on the box. It TRiggers drums. The pads are very responsive. They have a slight bounce to them which makes them pleasant to play. I find the best technique is to use individual fingers to trigger the pads. I've been using the SPD6 quite a lot and have to say that it very rarely misses a beat so despite it's shortcomings I find it invaluable for adding percussion that 'feels' like it's played and not programmed.
It probably is slightly over priced for what it is, especially considering some of it's shortcomings, but it's definitely the best midi hand drum pad for this price. If you like playing hand drums like bongos and want to be able to record custom drum performances really easily on a budget then this is the instrument for you.